Despite the potential of intergroup contact, there is little rigorous evidence about whether it can build lasting real-world behavior change in areas affected by conflict and ethnic violence. Evidence on the extent to which this tolerance can extend outside the intervention, or spillover to others in the community, is likewise sparse. To test whether positive and cooperative contact can improve relations across groups in post-conflict communities, Salma Mousa (Yale) randomly assigned displaced Christians either to play with Muslims, or fellow Christians, through a two-month soccer league in an ISIS-affected area of Iraq.